© Shamkant B. Navathe CC. © Shamkant B. Navathe CC Lesson 6 Enhanced Entity- Relationship and UML Modeling Copyright © 2004 Ramez Elmasri and Shamkant.

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Enhanced-ER (EER) Model Concepts Includes all modeling concepts of basic ER Additional concepts: subclasses/superclasses, specialization/generalization, categories, attribute inheritance The resulting model is called the enhanced-ER or Extended ER (E2R or EER) model It is used to model applications more completely and accurately if needed It includes some object-oriented concepts, such as inheritance

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Subclasses and Superclasses (1) An entity type may have additional meaningful subgroupings of its entities Example: EMPLOYEE may be further grouped into SECRETARY, ENGINEER, MANAGER, TECHNICIAN, SALARIED_EMPLOYEE, HOURLY_EMPLOYEE,… –Each of these groupings is a subset of EMPLOYEE entities –Each is called a subclass of EMPLOYEE –EMPLOYEE is the superclass for each of these subclasses These are called superclass/subclass relationships. Example: EMPLOYEE/SECRETARY, EMPLOYEE/TECHNICIAN

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Subclasses and Superclasses (2) These are also called IS-A relationships (SECRETARY IS-A EMPLOYEE, TECHNICIAN IS-A EMPLOYEE, …). Note: An entity that is member of a subclass represents the same real-world entity as some member of the superclass –The Subclass member is the same entity in a distinct specific role –An entity cannot exist in the database merely by being a member of a subclass; it must also be a member of the superclass Example: A salaried employee who is also an engineer belongs to the two subclasses ENGINEER and SALARIED_EMPLOYEE –It is not necessary that every entity in a superclass be a member of some subclass

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Attribute Inheritance in Superclass / Subclass Relationships An entity that is member of a subclass inherits all attributes of the entity as a member of the superclass It also inherits all relationships

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Specialization (1) Is the process of defining a set of subclasses of a superclass The set of subclasses is based upon some distinguishing characteristics of the entities in the superclass Example: {SECRETARY, ENGINEER, TECHNICIAN} is a specialization of EMPLOYEE based upon job type. –May have several specializations of the same superclass Example: Another specialization of EMPLOYEE based in method of pay is {SALARIED_EMPLOYEE, HOURLY_EMPLOYEE}.

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Specialization (2) Superclass/subclass relationships and specialization can be diagrammatically represented in EER diagrams Attributes of a subclass are called specific attributes. For example, TypingSpeed of SECRETARY The subclass can participate in specific relationship types. For example, BELONGS_TO of HOURLY_EMPLOYEE

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Generalization The reverse of the specialization process Several classes with common features are generalized into a superclass; original classes become its subclasses Example: CAR, TRUCK generalized into VEHICLE; both CAR, TRUCK become subclasses of the superclass VEHICLE. –We can view {CAR, TRUCK} as a specialization of VEHICLE –Alternatively, we can view VEHICLE as a generalization of CAR and TRUCK

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Generalization and Specialization (1) Diagrammatic notation sometimes used to distinguish between generalization and specialization –Arrow pointing to the generalized superclass represents a generalization –Arrows pointing to the specialized subclasses represent a specialization –We do not use this notation because it is often subjective as to which process is more appropriate for a particular situation –We advocate not drawing any arrows in these situations

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Generalization and Specialization (2) Data Modeling with Specialization and Generalization –A superclass or subclass represents a set of entities –Shown in rectangles in EER diagrams (as are entity types) –Sometimes, all entity sets are simply called classes, whether they are entity types, superclasses, or subclasses

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Constraints on Specialization and Generalization (1) If we can determine exactly those entities that will become members of each subclass by a condition, the subclasses are called predicate-defined (or condition-defined) subclasses –Condition is a constraint that determines subclass members –Display a predicate-defined subclass by writing the predicate condition next to the line attaching the subclass to its superclass

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Constraints on Specialization and Generalization (2) If all subclasses in a specialization have membership condition on same attribute of the superclass, specialization is called an attribute defined-specialization –Attribute is called the defining attribute of the specialization –Example: JobType is the defining attribute of the specialization {SECRETARY, TECHNICIAN, ENGINEER} of EMPLOYEE

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Constraints on Specialization and Generalization (3) If no condition determines membership, the subclass is called user-defined –Membership in a subclass is determined by the database users by applying an operation to add an entity to the subclass –Membership in the subclass is specified individually for each entity in the superclass by the user

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Constraints on Specialization and Generalization (4) Two other conditions apply to a specialization / generalization: 1. Disjointness Constraint: –Specifies that the subclasses of the specialization must be disjointed (an entity can be a member of at most one of the subclasses of the specialization) –Specified by d in EER diagram –If not disjointed, overlap; that is the same entity may be a member of more than one subclass of the specialization –Specified by o in EER diagram

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Constraints on Specialization and Generalization (5) 2. Completeness Constraint: –Total specifies that every entity in the superclass must be a member of some subclass in the specialization/ generalization –Shown in EER diagrams by a double line –Partial allows an entity not to belong to any of the subclasses –Shown in EER diagrams by a single line

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Constraints on Specialization and Generalization (6) Hence, we have four types of specialization/generalization: –Disjoint, total –Disjoint, partial –Overlapping, total –Overlapping, partial Note: Generalization usually is total because the superclass is derived from the subclasses.

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Specialization / Generalization Hierarchies, Lattices and Shared Subclasses (1) A subclass may itself have further subclasses specified on it Forms a hierarchy or a lattice Hierarchy has a constraint that every subclass has only one superclass (called single inheritance) In a lattice, a subclass can be subclass of more than one superclass (called multiple inheritance) In a lattice or hierarchy, a subclass inherits attributes not only of its direct superclass, but also of all its predecessor superclasses

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Specialization / Generalization Hierarchies, Lattices and Shared Subclasses (2) A subclass with more than one superclass is called a shared subclass Can have specialization hierarchies or lattices, or generalization hierarchies or lattices In specialization, start with an entity type and then define subclasses of the entity type by successive specialization (top down conceptual refinement process) In generalization, start with many entity types and generalize those that have common properties (bottom up conceptual synthesis process) In practice, the combination of two processes is employed

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Categories or UNION TYPES (1) All of the superclass/subclass relationships we have seen thus far have a single superclass A shared subclass is subclass in more than one distinct superclass/subclass relationships, where each relationships has a single superclass (multiple inheritance) In some cases, need to model a single superclass/subclass relationship with more than one superclass Superclasses represent different entity types Such a subclass is called a category or UNION TYPE

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Categories or UNION TYPES (2) Example: Database for vehicle registration, vehicle owner can be a person, a bank (holding a lien on a vehicle) or a company. –Category (subclass) OWNER is a subset of the union of the three superclasses COMPANY, BANK, and PERSON –A category member must exist in at least one of its superclasses Note: The difference from shared subclass, which is subset of the intersection of its superclasses (shared subclass member must exist in all of its superclasses).

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Formal Definitions of EER Model (1) Class C: A set of entities; could be entity type, subclass, superclass, category. Subclass S: A class whose entities must always be subset of the entities in another class, called the superclass C of the superclass/subclass (or IS-A) relationship S/C: S ⊆ C Specialization Z: Z = {S1, S2,…, Sn} a set of subclasses with same superclass G; hence, G/Si a superclass relationship for i = 1, …., n.

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Formal Definitions of EER Model (2) G is called a generalization of the subclasses {S1, S2,…, Sn} Z is total if we always have: S1 ∪ S2 ∪ … ∪ Sn = G; Otherwise, Z is partial. Z is disjoint if we always have: Si ∩ S2 empty-set for i ≠ j; Otherwise, Z is overlapping.

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Formal Definitions of EER Model (4) Subclass S of C is predicate defined if predicate p on attributes of C is used to specify membership in S; that is, S = C[p], where C[p] is the set of entities in C that satisfy p A subclass not defined by a predicate is called user-defined Attribute-defined specialization: if a predicate A = ci (where A is an attribute of G and ci is a constant value from the domain of A) is used to specify membership in each subclass Si in Z Note: If ci ≠ cj for i ≠ j, and A is single-valued, then the attribute-defined specialization will be disjoint.

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Formal Definitions of EER Model (3) Category or UNION type T –A class that is a subset of the union of n defining superclasses D1, D2,…Dn, n>1: T ⊆ (D1 ∪ D2 ∪ … ∪ Dn) A predicate pi on the attributes of T. –If a predicate pi on the attributes of Di can specify entities of Di that are members of T. –If a predicate is specified on every Di: T = (D1[p1] ∪ D2[p2] ∪ … ∪ Dn[pn] –Note: The definition of relationship type should have 'entity type' replaced with 'class'.

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Alternative Diagrammatic Notations Symbols for entity type / class, attribute and relationship Displaying attributes Displaying cardinality ratios Various (min, max) notations Notations for displaying specialization / generalization

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Data Modelling - The Basics Fundamental Principle of Modeling: Data Abstraction Basic Process of Modeling Define building blocks for holding groups of data Use rules of a data model to establish relationships among blocks Add constraints - structural/ semantic

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Fundamental Steps of Data Modeling 1 Inputs to Data Modeling 2 The Process of Modeling 3 Data Modeling Abstractions 4 Classification 5 Aggregation 6 Identification 7 Generalization 8 Coverage Constraints in Generalization 9 Cardinality and Participation Constraints

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Inputs to Data Modeling l Using the products of requirements analysis l Verbal and written communication among users and designers l Knowledge of meaning of data – Existing Programs – Existing Files – Existing Documents – Existing Reports l Application Planning / Documentation and Design

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Overall Process of Modeling l Abstraction l Use of some modeling discipline (Data Model) l Use of a representation technique Language Diagramming Tools l Analysis of business rules/semantic constraints (these are typically beyond the capability of the data model)

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Types of Abstractions ClassificationA is a member of class B AggregationB,C,D are aggregated into A A is made of/composed of B,C,D GeneralizationB,C,D can be generalized into A, B is-an A, C is- an A, D is-an A SpecializationA can be specialized into B,C,D B, C, D are specialization of A

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Classification Abstraction l Relationship between a class and its members John Smith, Sheela Patel, and Peter Wang are all employees. They are all members of a class: EMPLOYEE class EMPLOYEE John SmithPeter Wang Sheela Patel Each individual employee is a member of the class EMPLOYEE

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Classification Abstraction (contd.) January, February etc. are members of the class “MONTH” Represents “member-of” relationship In object-oriented modeling : MONTH : an Object type or class January … December : objects that belong to class MONTH MONTH JanuaryDecemberFebruary Exhaustive enumeration of members:

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Classification - Class Properties l Collection of similar entities or concepts into a higher level concept l EMPLOYEE class collects all employees into one class l A class has properties called “class properties” l EMPLOYEE class has class properties - e.g., average salary, total number of employees l Each member has values for own properties (e.g. name, address, salary): called member properties

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Aggregation Abstraction Defines a new class from a set of classes which are identified as components of the root class CAR Chasis Other Systems Drive-train represents IS-PART-OF (component) relationship Root class: CAR Component Classes: Chassis, Drive-Train, Other Systems, Wheels Root class: Wheels Component Classes: Tires, Tubes, Hub-Caps Wheels Tires Hub-Caps Tubes

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Classification and Aggregation Classification and Aggregation are used to build schemas Example: class Person Representation: Person Name Gender Position RamJohnCarlos MaleFemaleManagerEmployee 1. Name, Gender, and Position are aggregated into Person. They are classes themselves. 2. Ram, John, Carlos are classified into Name. Name is a classification of Ram, John, Carlos.

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Two Contexts for Aggregation Aggregate two or more classes into a higher level concept. It may be considered a relationship or association between them. Context1: CAR is an aggregate (composition) of Chassis, Drive-train, Other Systems, Wheels. Context 2: OWNERSHIP is an aggregate (relationship) of CAR and OWNER OWNERSHIP CAROWNER

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Identification Identifies one concept (an instance of it) from another concept. BUILDING ROOM Name Number Identifies

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Generalization Abstraction Defines a set-subset relationship between a class and a set of member classes. Establishes a mapping (or a relationship) from the generic class to the member class (or subclass, or subset class). EMPLOYEE StaffManagerEngineer GENERIC CLASS: EMPLOYEE MEMBER CLASS: Engineer, Staff, Manager Implies that all properties associated with the Employee class are inherited by the three leaf classes.

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Data Abstraction (contd.) Process of hiding (suppressing) unnecessary details so that the high level concept can be made more visible. This enables programmers, designers, etc., To communicate easily and to understand the application’s data and functional requirements easily. TYPES OF ABSTRACTION Classification:IS-A-MEMBER-OF Aggregation:IS-MADE-OF, IS-ASSOCIATED-WITH Composition:IS-MADE-OF (similar to aggregation) (A COMPRISES of B,C,D) Identification:IS-IDENTIFIED-BY Generalization:IS-AIS-LIKEIS-KIND-OF

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Coverage Constraints for Generalization Abstraction TYPE 1 : TOTAL vs. PARTIAL coverage Total: The coverage is total if each member of the generic class is mapped to at least one member among the member classes Partial: The coverage is partial if there are some member(s) of the generic class that cannot be mapped to any member among the member classes STUDENT GraduateSpecialUndergraduate (t) total EMPLOYEE HourlySalaried (t) total

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Coverage Constraints for Generalization Abstraction (contd.) Partial Coverage Constraint examples: STUDENT Fellowship Student Scholarship Student (p) partial EMPLOYEE ScientistEngineer (p) partial

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Coverage Constraints for Generalization Abstraction (contd.) TYPE 2: DISJOINT VS. OVERLAPPING (Disjointedness Constraint) DISJOINT constraint: A member of the generic class is mapped to one element of at most one subset class. OVERLAPPING constraint: There exists some member of the generic class that can be mapped to two or more of the subset classes. STUDENT ForeignAmerican (t, d) total, disjoint STUDENT Research AssistantGraduate (p, o) partial, overlapping Aid RecipientForeign

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Coverage Constraints for Generalization Abstraction (contd.) More examples of different combinations: VEHICLE VanCar (t, o) total, overlapping Two-wheelerThree-wheeler EMPLOYEE Technical Stuff (p, d) partial, disjoint Non-technical StuffManager Truck

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Cardinality Constraints Cardinality Constraint: Quantification of the relationship between two concepts or classes (a constraint on aggregation) MINIMUM (A,B) = n At a minimum, one instance of A is related to at least n instances of B. n = 0MIN(A,B) = 0MIN(Person, Car) = 0 n = 1MIN(A,B) = 1MIN(Cust, Ship-address) = 1 n = inf.MIN(A,B) = inf.NOT POSSIBLE n = x (fixed)MIN(A,B) = xMIN(Car, Wheels) = 4

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Cardinality Constraints (contd.) MAXIMUM (A,B) = n At a maximum, one instance of A is related to at least n instances of B. n = 0MAX(A,B) = 0DOES NOT ARISE n = 1MAX(A,B) = 1 MAX(Cust, Ship-address) = 1 n = inf.MAX(A,B) = inf.MAX(Cust, Orders) = inf. n = x (fixed)MAX(A,B) = xMAX(Stud, Course) = 6

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Participation Constraints MIN (A,B) = 0Optional Participation MIN (A,B) = 1Mandatory Participation MAX (A,B) = 0No Participation MIN (A,B) = x, MAX (A,B) = y Range Constrained Participation

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Ramez Elmasri and Shamkant Navathe Summary of Modeling Concepts ABSTRACTIONS l CLASSIFICATION l AGGREGATION (COMPOSITION AND ASSOCIATION) l IDENTIFICATION l GENERALIZATION AND SPECIALIZATION CONSTRAINTS l CARDINALITY (Min. and Max) l PARTICIPATION l COVERAGE (Total vs. Partial, Exclusive vs. Overlapping)

© Shamkant B. Navathe CC. © Shamkant B. Navathe CC Lesson 6 Enhanced Entity- Relationship and UML Modeling Copyright © 2004 Ramez Elmasri and Shamkant.

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© Shamkant B. Navathe CC. © Shamkant B. Navathe CC Lesson 6 Enhanced Entity- Relationship and UML Modeling Copyright © 2004 Ramez Elmasri and Shamkant.

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